From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id DEAE1101FE for ; Mon, 7 Aug 2023 13:07:07 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1691413626; h=from:from:reply-to:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=wTw5UGHZz4e2SdP2OePYtf5FEiTOr08NgMVHrTIjIdY=; b=i+YSWZcQBfhBd4CvvrH4LD7YfWtDSORKDQOfndvnuDxSNNMKwis5+IQD2M0eNxRIjzfxyk g1KupK6F7mque85VW3/BViuNq51hmu4gNqAfarU2dwvVjOjLtwk5Q6tt0gk9kfe0YdqvsK /Vx5QlfnCsULFpzouzC96LbUvthsfTg= Received: from mimecast-mx02.redhat.com (66.187.233.73 [66.187.233.73]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-684-8FRjDLUHNAWmNwU-04hwKw-1; Mon, 07 Aug 2023 09:07:01 -0400 X-MC-Unique: 8FRjDLUHNAWmNwU-04hwKw-1 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.rdu2.redhat.com [10.11.54.4]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 6B69B3C108CB; Mon, 7 Aug 2023 13:07:00 +0000 (UTC) Received: from tucnak.zalov.cz (unknown [10.45.224.18]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 1A81C2026D4B; Mon, 7 Aug 2023 13:06:59 +0000 (UTC) Received: from tucnak.zalov.cz (localhost [127.0.0.1]) by tucnak.zalov.cz (8.17.1/8.17.1) with ESMTPS id 377D6th33645769 (version=TLSv1.3 cipher=TLS_AES_256_GCM_SHA384 bits=256 verify=NOT); Mon, 7 Aug 2023 15:06:55 +0200 Received: (from jakub@localhost) by tucnak.zalov.cz (8.17.1/8.17.1/Submit) id 377D6pvb3645768; Mon, 7 Aug 2023 15:06:51 +0200 Date: Mon, 7 Aug 2023 15:06:51 +0200 From: Jakub Jelinek To: Florian Weimer Cc: Marco Elver , Andrew Morton , Kees Cook , Guenter Roeck , Peter Zijlstra , Mark Rutland , Steven Rostedt , Marc Zyngier , Oliver Upton , James Morse , Suzuki K Poulose , Zenghui Yu , Catalin Marinas , Will Deacon , Nathan Chancellor , Nick Desaulniers , Tom Rix , Miguel Ojeda , linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev, linux-kernel@vger.kernel.org, llvm@lists.linux.dev, Dmitry Vyukov , Alexander Potapenko , kasan-dev@googlegroups.com, linux-toolchains@vger.kernel.org Subject: Re: [PATCH v2 1/3] compiler_types: Introduce the Clang __preserve_most function attribute Message-ID: Reply-To: Jakub Jelinek References: <20230804090621.400-1-elver@google.com> <87il9rgjvw.fsf@oldenburg.str.redhat.com> <87h6pbf2f8.fsf@oldenburg.str.redhat.com> Precedence: bulk X-Mailing-List: kvmarm@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <87h6pbf2f8.fsf@oldenburg.str.redhat.com> X-Scanned-By: MIMEDefang 3.1 on 10.11.54.4 On Mon, Aug 07, 2023 at 02:43:39PM +0200, Florian Weimer wrote: > > On Mon, Aug 07, 2023 at 02:24:26PM +0200, Marco Elver wrote: > >> > | If the arguments are passed in callee-saved registers, then they will > >> > | be preserved by the callee across the call. This doesn’t apply for > >> > | values returned in callee-saved registers. > >> > | > >> > | · On X86-64 the callee preserves all general purpose registers, except > >> > | for R11. R11 can be used as a scratch register. Floating-point > >> > | registers (XMMs/YMMs) are not preserved and need to be saved by the > >> > | caller. > >> > | > >> > | · On AArch64 the callee preserve all general purpose registers, except > >> > | X0-X8 and X16-X18. > >> > > >> > Ideally, this would be documented in the respective psABI supplement. > >> > I filled in some gaps and filed: > >> > > >> > Document the ABI for __preserve_most__ function calls > >> > > >> > >> Good idea. I had already created > >> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110899, and we need > >> better spec to proceed for GCC anyway. > > > > "Registers used for passing arguments > > are preserved by the called function, but registers used for > > returning results are not." > > > > You mean just GPRs or also vector SSE or MMX registers? > > I think this is pretty clear for x86-64: > > | Floating-point registers (XMMs/YMMs) are not preserved and need to be > | saved by the caller. The above wording conflicts with that, so it should be clarified. 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